Inorganic salt mixtures phase change materials (PCM) for thermal energy storage

Naveed Hassan

For thermal energy storage, the most promising method that has been considered is the use of latent heat property to store energy in molten salt mixtures phase change material. Two binary salt mixtures LiCl(32 mol%)-LiOH(68 mol%) and CaCl2(58 wt%)-LiCl(42 wt%) were synthesised and characterized with a focus on thermophysical properties, thermal repeatability/stability, chemical stability, morphological formation, and distribution of elemental composition. Simultaneous Thermal Analyzer was utilized to determine thermophysical properties. LiCl(32 mol%)-LiOH(68 mol%) had melting and solidification temperature of 269 °C and 265 °C respectively. Additionally, the heat of fusion and heat of crystallization were recorded as 379 J/g and 375 J/g, respectively. The eutectic salt, CaCl2(58 wt%)-LiCl(42 wt%), possesses the appropriate melting temperature of 488 °C and a solidification temperature of 480 °C. The heat of fusion and heat of solidification were recorded by 206 J/g and 180 J/g, respectively. Thermal repeatability and thermal stability were analyzed for 30 heating/cooling cycles. LiCl(32 mol%)-LiOH(68 mol%) had a marginal change in the thermal properties, with a weight loss of < 1.5% being recorded. However, a considerable change in the heat of fusion and weight loss was observed from the CaCl2(58 wt%)-LiCl(42 wt%) samples, which demonstrates a relatively poor repeatability and weak thermal stability of the binary eutectic salt. Furthermore, an in-situ X-Ray Diffraction (XRD) shows the upper-temperature limit of the LiCl(32 mol%)-LiOH(68 mol%) salt to be at around 500 °C and limited changes in the peak corresponding to lithium oxide in decomposed sample representing good chemical stability. The decomposition behaviour of CaCl2(58 wt%)-LiCl(42 wt%) displays continuous weight loss, together with new phases to be identified, through the in-situ XRD, from the samples before and after thermal treatment demonstrating chemical instability. Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy confirmed the materials’ good morphology and elemental distribution, without detecting any other impurities. X-Ray Photoelectron Spectroscopy was conducted for both samples showing parent elemental spectra and adequate atomic composition. Overall, the results confirmed that LiCl(32 mol%)-LiOH(68 mol%) is a potential candidate material for energy storage applications. However, the poor thermal stability of CaCl2(58 wt%)-LiCl(42 wt%) limit its use in practical applications.

Inorganic salt mixtures phase change materials (PCM) for thermal energy storage

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